Hey there Snow_4,
Thanks for reaching out to the Apple Support Communities.
Just to confirm, when you say that the cellular signal on your iPhone 14 Pro Max is dropping, are you seeing No Service or Searching in the iPhone status bar? If so, we would recommend going through the steps listed in the following resource that can help with that specific issue: If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support
Check your coverage area
• Make sure that you're in an area with cellular network coverage.
• Turn cellular data off and then back on again. Go to Settings, then tap Cellular or Mobile Data. If you're using an iPad, you might see Settings > Cellular Data.
• If you're traveling internationally, make sure that your device is set up for data roaming. Go to Settings > Cellular > Cellular Data Options > Data Roaming.
Restart your iPhone or iPad
Restart your device. If you're not sure how to do this, follow these steps to restart your iPhone or restart your iPad.
Check for a Carrier Settings update
To manually check for and install a carrier settings update:
1. Make sure that your device is connected to a Wi-Fi or cellular network.
2. Tap Settings > General > About. If an update is available, you'll see an option to update your carrier settings.
3. To see the version of carrier settings on your device, tap Settings > General > About and look next to Carrier.
If you insert a new SIM card into your iPhone or iPad, you need to download the carrier settings for your new carrier.
Update your iPhone or iPad
Update your iPhone or iPad to the latest version of iOS or iPadOS.
If still having issues after going through the additional steps in the above resource, the next best option would be to reach out to your carrier who may be able to provide some additional information or possible troubleshooting steps.
Keep us updated on the results.
Take care.